undertray for downforce???

[Anonymous]

hey all, i am building a fast car thats gonna be used for the race track and the street, so i dont want to build up massive RICERIIIIICEE-BAD OK LOL

so i want to make a ground effect, full length under tray for the car, anyone have anyideas? or some websites i could look at?

cheers.joe.

 

[xctasy]

That dude Sven who made the twin SC14 Super Charged Clevo XF. He made one for his. (He also made hydro-pneumatic suspension with dropped spindles too, but I digress yet again).

A quick Note. Any thing that increases air speed under the car will make it lift. By smoothening it you will create lift, like a aircraft wing. The main aim is to slam it down, and divert wind around it. Engine heat, significant on a turbo, must be directed out of the engine bay, and I would say a proper ground affect system is going to be hard pressed to accomodate your needs.

That blue XF ute wasn't ground effect, but reduced the underbody to a smooth punt rather than the awful gutted amalgam of braces the X-bodies had. EA's are a bit smoother under there, but not a lot. The thing to be aware of is that a normal EA is quite clean at about 0.36 cd for a lowered S-pack. If you slam it, it will drop to 0.32 if you drop it 100mm. Pretty easy since the stockers sat so high. The fontal area is very slightly reduced.

The undertray would take it down to 0.30 easily, but the stability drops. If you go for ground effects, forget a good cd figure. Best option is to duplicate an early DJR EB body kit, and make a big rivited or deus fasened alloy plate for the under body. However, it will raise the total wind resistance without out helping the cd. So you will loose top speed, but gain in stability.

Any four door with a profile like the EA would do well to have the blue EA GT351 showcar tail spoiler on it. Ford put lots of work into the standard 'strakes' which bent the air away from the backlight to stop hig-speed wander and sensitivity to cross winds. Any areodynamic aid will create drag unless you spend 200 hours in a wind tunnel perfecting it.

Have a good decko at what CRS is doing on Rods VP Commodore with that big-block Chev for lake racing. Its got a big tail on it to stablise it. Ugly, but efficient.

Ground effects isn't a valid concept for a road car unless you have wind tunnel time or a V8 Supercar kit you can copy.

 

[addo]

I always admired the Chaparral cars that "hoovered" themselves to the track.

 

[Anonymous]

i already have a vented bonnet, directing heat out into the incominf air stream , this will give me good down force, hot air rises, so when the cold air hits it, it should ramp up sharply and creating a downforce affect on the bonnet.

also, under the car, there is a big engine nappy, its a plate that extends to the back of the engine from the bottom of the front bumper, stoping any air getting up in the engine bay and using the bonnet as a big parachute.

i may make up a rear bar that diffusers that will speed the air up ar the rear of the car, makeing a low pressure area behind the car and sucking the arse end down, also i am thinking of a set of diffuses under the car (just behind the drivers foot well. that direct air out the side od the car, just in front of the the rear wheele, to reduce the air thats under the car.

oh and xecute... the car is down to it lowest street legal height i can go .. 100mm off the ground.

this car wil be be capable of cracking 300 kmph and i intend on streching its legs right out!!

any help is welcomed, strange ranger or some racing fellas on these boards may be able to help out.

cheers.joe.

 

[Anonymous]

found something..

i am mainly after an under tray myself..

the above is an undertray for a forumula ford race car.

above is a bmw race car front undertray..more info and pics at
http://www.bimmerworld.com/html/bimmerworld-e36-front-splitterundertray.htm

hope this helps you.

and some more drivell from my toughts on the matter-

you want to limit as much air as posible thats going under the car,

a front splitter, directs air over the top of the car, so having the car as low as posible will also reduce air going under neath it.

on the formula ford car, they have a pair of strakes to direct air to to side of the car (out under side skirts) just in frount of the rear wheels,

adding a rear bumper with ventri's will speed up the air exiting the rear of the car, creating a low pressure area behind the car, air traveling over the car will want to fill the low pressure area thus creating a sharp turn of air on the rear of the car..thus more down force.

a tray like the bimmer one above, would prevent air getting up under the bonnet and using it like a big parachute (read... create lift).

i think i will employ the following on my ea falcon...

i already have a vented bonnet, directing heat out into the incominf air stream , this will give me good down force, hot air rises, so when the cold air hits it, it should ramp up sharply and creating a downforce affect on the bonnet.

also, under the car, there is a big engine nappy, its a plate that extends to the back of the engine from the bottom of the front bumper, stoping any air getting up in the engine bay and using the bonnet as a big parachute.

i may make up a rear bar that diffusers that will speed the air up ar the rear of the car, makeing a low pressure area behind the car and sucking the arse end down, also i am thinking of a set of diffuses under the car (just behind the drivers foot well. that direct air out the side od the car, just in front of the the rear wheele, to reduce the air thats under the car.

oh the car is already down to it lowest street legal height i can go .. 100mm off the ground.

and.....

what i am thinking..

is (lucky i am a sheetmetal worker :mrgreen: )

a front bar that comes down to 4 or 5 inches of the ground,
on the under side of that a big alloy sheet that goes back to where the bell housing is, on a gradual gradient up to the floor level,

this plate would meet with an other that went right back to the diff, with simular strakes to what is depicted in the photo of the formula ford car, to disperse air out the sides of the car in frontof the back wheels,

another plate would be behind the diff with strakes in it that match up to the rear bar that has difuses on it to speed the air up,

the air that enter the radiator and into the engine bay would be deflected up into the bonnet vent i will be makeing in the bonnet,

this way, i can get max down force with out an attention attracting wing on the back, and with out a massive front end over hang on the front bar, so basicly any air that hits the front of the car will-

50-60% of air will go over the top of the car
20-30% will go thru the radiator into the duct that feed air up over the bonnet thus creating a downforce effect on the front
the other 10-20% of air will be channeled and guided under the car to create a down force effect on the arse end

who knows it may just work.

but first i have to sort out its spray job and interior then assemble the bloody thing, before i can test out my aerodynamic theories.


ps. do a google search for undertray came up with a lot of bike shit, but theres car stuff in there as well.

cheers.joe.

 

[Thad]

Down force design for under car, four points :
1. Minimum enter area, a splitter type chin spoiler dictates what air goes under and what air goes over. Minimum grille opening and headlight fairings eliminate trapped air and varing compression impulses.
2. Side deflector or seals to restrict side entry of air.
3. Larger exit area than entry, cross sectional flow area to increase front to back.
4. Smooth as possible undertray / belly pan to minimize trublence and
maintain air velocity under car.

Diffusser are mis-named and have the opposite function. They are exit nozzles designed and shaped to keep exiting air channelized and maintain exit velocity much the same as a lip spoiler compresses boundary so velocity will increase for clean seperation after leaving surface..

 

[Anonymous]

A quick Note. Any thing that increases air speed under the car will make it lift.

Not always tru, dude. Check out that Bernoulli guy. You can demonstrate by using an air chuck to blow a high speed streem twix forefinger and thumb. the airflow will create suction, not pressure. On a car, you maximize that by containing the flow with side skirts.

 

[Thad]

VENTURI, Bernoulli's law and all that, And it is all real simple.

As air flow velocity increases pressure decreases. eg carb venturi.
The air space between the under tray and the ground should bethought of and designed as a venturi, with the air velocity / pressuse drop greatest at the dynamic balance point.

Jim Hall's Chaparrals started with a ground effect venturi system with sliding seals and sealing brushes to eliminate side entry of as much air as possible. Later on the sucker car used a snowmobile engine turning a fan evacuate air from under the car and discharge into the aero drag behind.
Hall was far ahead of everybody; fiberglas monocoque, auto trans, air flow control on topsurface and under car, downforce wing linked to brakes, sliding sealed ground effect and the sucker. The sliding seals, articulated wing and sucker motor were outlaw as movible aero devices. As fast as Hall could come up with sometime it was outlawed.